The present invention relates to four-color light-emitting devices.
Full color organic electroluminescent (EL) devices, also known as organic light-emitting devices or OLED, have recently been described that are constructed of pixels having four subpixels that are red, green, blue, and white in color. Such an arrangement is known as an RGBW design (see U.S. Patent Application Publication 2002/0186214). This type of organic EL device is typically constructed using a white organic EL emitting layer with red, green, and blue color filters. The white subpixel area is left unfiltered. This design has the advantage of lower power consumption and current density, compared to a three-color filtered white-emitting organic EL device when used in applications, which make frequent use of white backgrounds such as the typical personal digital assistant or computer display.
Organic EL devices are frequently driven by active matrix circuitry. Several circuitry layouts are known in the art. The most common circuit layout is known as a stripe pattern, in which each pixel contains several subpixels aligned in a row. The driving circuitry for a stripe design consists of a select line to select each row of pixels. Data lines run perpendicular to the select line and are used to determine the brightness of each pixel in the row. To operate a stripe pattern active matrix organic EL device, each row is selected by applying a voltage to the select line, and the brightness level for each subpixel is controlled by a voltage signal held on the data line. Examples of stripe patterns are shown in U.S. Pat. No. 6,281,634.
A second type of circuitry layout is known as a delta pattern. In a delta pattern, the subpixels are not aligned in a row, but are instead laid out in a triangular pattern. Examples of delta patterns are shown in U.S. Pat. No. 6,456,013 and U.S. Patent Application Publication 2002/0070909. Delta patterns are frequently preferred over stripe patterns because the three subpixels are closer to one another than in a stripe, which can provide a preferred appearance to the viewer.
However, conventional delta designs are only useful for devices that have three different color subpixels and therefore are not appropriate to a four-color display. Conventional stripe pattern circuits, if applied to a four-subpixel design, would require the subpixels to be arranged in a 1xc3x974 matrix. This approach results in the first and fourth subpixels being spaced far from one another, which results in a less preferred appearance to the viewer. Therefore, a pixel circuit that arranges the subpixels closer together is required.
The addition of a fourth subpixel element increases the number of active matrix circuit components (such as transistors and capacitors) and connection lines (such as the data and power lines) required for each pixel. In a bottom-emitting device, that is a device in which light emerges through the substrate that includes the circuitry, the circuitry can block some of the light emission. The ratio of the area of light emission to the area of non-emission is known as aperture ratio. Higher aperture ratio is desirable, as lower aperture ratio devices will require increased current density to achieve the desired average brightness of light emission. It is known that organic EL devices degrade more rapidly at higher current densities, decreasing the useful lifetime of the display. In a top-emitting device, that is a device in which light emerges from the direction opposite the circuitry, the aperture ratio is not affected by an increased number of circuit components and connection lines. However, the number of circuit components and connection lines for either top- or bottom-emitting devices will limit the minimum size of a pixel that can be constructed and therefore the overall resolution of a design. Therefore, new pixel designs that reduce the surface area used by the circuit components and connection lines are required.
It is therefore an object of the present invention to provide improved drive circuitry for a four-color organic light-emitting device having pixels, which emit light.
This object is achieved by a four-color organic light-emitting device having pixels which emit light, comprising:
a) a substrate;
b) pixels arranged in rows and columns and each pixel including groups of four subpixels disposed over the substrate and wherein each subpixel includes spaced apart first and second electrodes;
c) organic EL media disposed between the first and second electrodes of each subpixel;
d) drive circuitry disposed relative to the organic EL media over the substrate and arranged to drive each group of four subpixels and having an electrical connection to the first electrode corresponding to each subpixel, and wherein
e) the drive circuitry for each group of four subpixels including four data lines, two power lines, and one select line, the four data lines being shared for each column of the array of pixels, and the select line being shared for each row of the array of pixels.
The invention has the advantage over conventional designs, such a stripe and delta circuits, in that the four subpixels can be arranged and driven in a 2xc3x972 matrix. This invention also reduces the surface area of the circuit components and connections. This allows for either an improved aperture ratio or a greater possible number of pixels per unit area.